The invention relates generally to ionic polymers and copolymers made from ionic liquids, referred to herein as poly(ionic liquid)s, and, more specifically, to ionic polymers and copolymers used to absorb electromagnetic energy in the radio frequency band, particularly microwave and radar band radiation.
Ionic liquids, which are organic salts that become liquids usually below about 250° C., have attracted attention because of their unique chemical and physical properties and a wide application potential [Huddleston, J. G.; Willauer, H. D.; Swatloski, R. P.; Rogers, R. D. Chem Commun 1998, 16, 1765-1766; Wasserscheid, P.; Keim, W. Angew Chem Int Ed 2000, 39, 3772-3789; Welton, T. Chem Rev 1999, 99, 2071-2084; Rogers, R. D. and Seddon, K. R. (ed), Ionic Liquids as Green Solvents: Progress and Prospects, American Chemical Society: Washington, D.C., 2003; Ding, J.; Zhou, D.; Spinks, G.; Wallace, G; Forsyth, S.; Forsyth, M.; MacFarlane, D. Chem. Mater 2003; 15, 2392-2398; Liang, C.; Yuan, C-Y.; Warmack, R. J.; Barnes, C. E. and Dai, S. Anal Chem 2002, 74, 2172-2176; Pernak, J.; Czepukowicz, A.; Poz´niak, R. Ind Eng Chem Res 2001, 40, 2379-2383].
Conventional liquids are molecular, being constituted of molecules, regardless of whether they are polar or non-polar. Ambient temperature ionic liquids are comprised of ions that allow them to behave in a very different manner to conventional molecular liquids when they are used as solvents. The physical properties of ionic liquids can be very different from conventional liquids and by combining different anions and cations in an ionic liquid it is possible to synthesize a library of different ionic liquids each with specific properties.
Microwave absorbing materials have many applications such as noise suppression materials in data transmission, mines detection, artificial human tissue, and radar absorbing materials in military applications. Polymeric materials are of especial interest because of their light weight, easy application and easy fabrication into various shapes such as coating. However, no conventional polymer has been found to have strong microwave absorption properties. Accordingly, it would be advantageous to provide a polymeric material that can be easily manufactured and formed into a variety of shapes that also has a high absorbance of microwave type and other radio frequency radiation.